Acute toxicity and histopathological changes in liver and gill epithelium of African Catfish (Clarias gariepinus) juveniles exposed to mercuric chloride

Abstract

Acute toxicity of mercuric chloride (HgCl₂) on Clarias gariepinus juveniles was assessed. A total of 180 fish of mean weight 31.07±1.23 g and mean length 19.50±0.50 cm were divided into six groups of ten fish each of three replicates. The juveniles were exposed to different concentrations of 0.00 (control), 1.20, 1.40, 1.60, 1.80 and 2.00 mg/L for a period of 96 hours. Juveniles in the control group survived while those exposed to 1.80 and 2.00 mg/L died. Determination of 96 hours LC₅₀ was carried out by computing mortality results in Probit program of SPSS (version 17.0). Median lethal concentration was 1.492 mg/L with lower and upper confidence limits of 1.44 mg/L and 1.59 mg/L respectively at 95%. Liver and gill samples were collected after 4 days of exposure to HgCl₂ and lesions were analyzed by light microscopy. Main histopathological changes observed in gills exposed to highest concentration were edema, lifting of lamellar epithelia and an intense vasodilatation of lamellar vascular axis. Although less frequent, lamellar fusion caused by filament epithelium proliferation and some lamellar aneurisms were also found. Liver of control group exhibited a quite normal architecture, while fish exposed to HgCl₂ showed vacuolation and necrosis.

Keywords: Toxicology, histopathology, mortality, mercuric chloride, Clarias gariepinus